1. Field of the Invention
The present invention elates to an electronic component comprising one or more coils buried in a chip.
2. Description of the Related Art
FIG. 2 shows a side sectional view of a laminated inductor as a conventional electronic component on this head.
In FIG. 2, 20 is a laminated inductor comprising a rectangular-parallelepiped-shaped chip 21 of a magnetic substance material, a spiral coil 22 buried in the chip 21, and a pair of terminal electrodes 23 provided at the longitudinal ends of the chip 21. The winding center line, i.e., longitudinal axis, Y of the coil 22 is orthogonal to a line joining the terminal electrodes 23 together (extending in the longitudinal direction of the chip), and the end of the coil 22 is guided out to the end surface of the chip where it is connected to the respective terminal electrode 23.
To mount the laminated inductor 20 on a conductor pattern on a circuit board, two orientations are available in which the winding center line (Y) of the coil 22 is perpendicular to the mounting surface of the circuit board (Z) as shown in FIG. 3 and in which winding the center line (Y) of the coil 22 is parallel with the mounting surface of the circuit board (Z) as shown in FIG. 4.
There is a difference in inductance between the mounting orientations in FIGS. 3 and 4 due to the different locational relationship between the coil 22 and the circuit board (Z) resulting in a difference in magnetic reluctance to magnetic fluxes outside the chip. In particular, in a laminated inductor using a chip material of a lower relative magnetic permeability, the difference in mounting orientation causes a significant difference in magnetic reluctance and thus a relatively large difference in inductance.
To solve such a problem, a laminated inductor has been proposed in which the orientation of the winding center line of the coil relative to the surface of the circuit board remains unchanged regardless of the mounting orientation (Japanese Patent Application Laid-Open No. 8-55726).
This laminated inductor is generally called a vertically laminated inductor wherein a laminated structure is formed in the direction of a line joining the terminal electrodes together as shown in FIGS. 5 to 7.
A chip 31 in a vertically laminated inductor 30, which is shown in FIGS. 5 to 7, is formed by laminating a top-layer sheet (A) of a magnetic material, coil-layer sheets (B1) to (B4) of a magnetic material, and a bottom-layer sheet (C) of a magnetic material. A leadout conductor (Pa) is formed in the top layer-sheet (A) of a magnetic material in such a way as to overlap a via hole (h). Four types of approximately-U-shaped coil conductors (Pb1) to (Pb4) are formed in the coil-layer sheets (B1) to (B4) of a magnetic material in such a way that their ends overlap the via hole (h). In addition, a rectangular leadout conductor (Pc) is formed in the bottom-layer sheet (C) of a magnetic material in such a way as to overlap the via hole (h). Furthermore, terminal electrodes 33 are formed at the respective ends of the chip 31 in the lamination direction to constitute the vertically laminated inductor 30.
The coil conductors (Pb1) to (Pb4) are connected together via the via hole (h) to form the coil 32, and the respective ends of the coil 32 are connected to the terminal electrodes 33 via leadout conductors 34a and 34b consisting of leadout conductors (Pa) and (Pc) formed in the top- and bottom-layer sheets (A) and (C) of a magnetic material.
In the vertically laminated inductor 30 of the configuration shown in FIGS. 5 to 7, when a current flows through the inductor, two fluxes are generated; one of them is parallel with the winding center line (Y) of the coil 32, while the other rotates around the leadout conductors 34a and 34b. These magnetic fluxes form the inductance of the chip.
When, however, the laminated inductor 30 is mounted on the circuit board (Z), there is a difference in distance between the leadout conductor 34a or 34b and the circuit board (Z), between the mounting orientation shown in FIG. 8 and the mounting orientation shown in FIG. 9 in which the inductor is vertically revered. Consequently, there is a difference in magnetic reluctance to magnetic fluxes generated around the leadout conductors 34a and 34b, resulting in a difference in inductance depending on the mounting orientation.